Carrier-wave transmission



March 30 1926. v ,1,57 s,s46

, -H.w. NICHOLS CARRIER WAVE TRANSMISSION- Filed August 24, 1921 //7 veh fok: I Harv/d VM/Vlbfi'o/s.

Patented Mar. 30, 1926.

HAROLD W. NICHOLS, OF MAPLEWOOD, NEW JERSEY, ASSIGNOR TRIO COMPANY, INCORPORATED, YORK.

TO WESTERN ELEC- OF NEW YORK, N. Y., A CORPORATION OF NEW CARRIER-WAVE TRANSMISSION.

Application, filed August 24, 1921. Serial No. 495,100.

line at the frequencies of the carrier waves whereby incoming and outgoing carrier transmission channels maybe conjugately associated with the power transmission line. Another feature of the invention relates to a current limiting apparatus for limiting the magnitude of disturbing currents which may be impressed upon the carrier receiving apparatus.

According to this invention, an alternating current power transmission line is connected to ground at a neutral point. The ground conductor is also connected to a network which simulates the impedance of the transmission line at the carrier wave frequencies. The carrier wave transmitting and receiving apparatus are conjugately connected with respect to each other to the ground connection of the power line. The carrier receiving apparatus is provided with a current limiting device to exclude therefrom excessive currents resulting from disturbing energy.

In the drawing, Fig. 1 illustrates one terminal of a system embodyin" the invention in which carrier wave signaling apparatus is composited with a three-phase alternating current power transmission system, and Fig. 2 illustrates a modification of the arrangement of Fig. 1 in which certain elements of the carrier transmitting and receiv ing apparatus are combined.

Referring to Fig. 1, a source '1 of threephase alternating power current is associated with a three-phase transmission line 2, by means of a transformer 3. Each of the three conductors of the transmission line 2- is connected through an individual capacity element 4 to a neutral point 5. The ground receiving c annel 10.

connection is made from the neutral'point 5 through the primary windings of a balanced trans ormer 6 and a balancing network N. Each of the capacity elements 4 offers such high-reactance to currents of the frequency of the power currents produced by source 1,

. as to present an extremely high impedance thereto. Balancing network N is designed to simulate the impedance of the transmission system beyond the neutral point 5 at the frequencies of all the carrier waves which are to be transmitted thereoverf A two-way transmission circuit 7, which may be an ordinary telephone or other signal circuit, is terminated in a balancing network N, which simulates the impedence of the circuit 7 at the frequencies of all of the signal currentsto be transmitted there over. The circuit 7 is associated by means of the balanced transformer or hybrid coil 8 of Well known type with the carrier wave transmittin channel 9 and the carrier wave The carrier wave transmitting channel includes a thermionic oscillator Owhich comprises a three-element electric discharge device 11, preferably of thehighly evacuated type, togetherwith its associated circuits. The oscillatory circuit of this oscillator may be traced from the anode of the device 11 by way of capacity 12 and inductance 13 .to ground. The transmission system and its counterpart N, to which the anode is connected at the midpoint of the primary of the balanced transformer 6, constitute, in eflect, a reactance element which completes the oscillatory circuit from ground back to the anode. The device 11 is supplied with space current by a source E, and with filament heating current by a current source E... The oscillator O is associated with the variable impedence device 14 consisting of a three-element thermionic discharge device supplied with space current from the source E The variable impedance device and the oscillator together with constant current choke coil 15 m their common space current path, constitute a modulating system of the well known Heising constant current type described in the article entitled Radio telephony at page 360 of the Proceediligs of the American Institute of Electrical ngineers, vol. 38.

#3. Low frequency signal currents or other impulses originating in circuit 7 i are impressed upon the input circuit of variable impedance device 14 to cause the oscillator O to supply correspondingly modulated carrier waves to the transmission system 2.

, trio discharge device having two electrodes,

' waveapparatus is associated with a each preferably heated in the manner of the well known vacuum tube cathode. The maximum electron emission from these cathodes may be determined by the temperature at which they operate, and this in turn may be regulated by varying the electromotive forces of the heating sources 18. Since current in circuit 16 must traverse electric discharge device 17 as an electron stream from one hot filament acting as a cathode to theother acting as an anode, it is possible tolimit the maximum intensity of the current in circuit 16 to any desired value. It follows that if an excessive E. M. F. is impressed upon the secondary winding of transformer 6, the current in circuit 16 will not exceed the preassigned limiting value. Receiving circuit 16 may be tuned in the ordinary manner by means of the variable capacity element 19. A demodulating device 20, preferably of the well known three-element thermionic type, is connected to circuit 16 .and serves to supply demodulated currents or low frequency signal waves to circuit 7 It is accordingly possible to carry on a'twoway telephone conversation from a local circuit-7 to a similar remote circuit which is likewise associated with the power transmission system 2, by means of carrier wave transmitting and receiving apparatus.

Fig. 2 illustrates an arrangement in which a local transmitting station is connected to a three-phase power transmission system.-

As in the arrangement in Fig. 1, the carrier grounded conductor connected to a neutra point, but no attempt is made to balance the impedance of the transmission system. The grounded conductor includes the primary w nding of a transformer 26, the secondary winding of which is included serially in the space current circuit of a thermionic modulator M. Associated with the input circuit of the modulator M by means of transformers 27 and 28, respectively, are the thermionic oscillator 0 and the talks ing circuit 29. The oscillator 0 impresses carrier wave oscillations upon the modulator M and if speech waves heinipressed. upon the microphone of the circuit.

29, the circuitwill serve to impress speech currents upon the input circuit of modulator M to produce modulated carrier oscillations in the output circuit of the modulator. This modulating arrangement is essentially'the same in principle as that disclosed in the patent to Van der- Bijl, No. 1,350,752, patented August 24, 1920, and, therefore, needs no further explanation. The modulated carrier oscillations are impressed by transformer 26- upon the power transmission line 2.

Incoming carrier oscillations received over the transmission system 2 are impressed by the transformer 26 upon the anode-cathode circuit of the modulator M. This circuit operates in accordance with the principle of the well known Fleming valve to demodulate the incoming oscillations and to roduce lowfrequency currents correspon ing to those by which the incoming carrier waves were modified at the remote carrier station. These demodulated waves or low frequency currents are transmitted by a transformer 36 to the input circuit of thermionic amplifier A which amplifies these low frequency currents and supplies them to a translating device It which may be an ordinary telephone receiver. The modulator M serves not only to demodulate the incoming carrier currents, but also as a current limiting device to exclude excessive currents from the receiving amplifier A. Its current limiting function occurs in consequence of the fact that the alternating current which it is able. to transmit is limited to the maximum value which the electron stream emitted from the cathode may assume and the E. M. F. of theheating source 37 is so adjus d as to limit the electron stream to a predetermined magnitude.

Although the features of the invention have been disclosed in two distinct circuit arrangements, it should be understood that they are not limited thereto but are capable of application to electric transmission generally.

What is claimed is:

1. A power line, means for supplying power currents to said line for-transmission thereby, a network,means for transmitting carrier waves modifiedin accordance with speech, means for receiving carrier waves modified in accordance with speech, and means including a transformer for connecting said carrier wave transmitting means and carrier wave receiving means to both said line and said network and conjugately withrespect to each other at signal frequencies,

said network being designed to simulate the impedance of said line at all frequencies within agiven range including the freq encles of the carrier waves to .be transmitted and not including the frequencies of said power currents, whereby high voltages are prevented from being established at the windings of said transformer.

2. A power transmission line means for sin'lulating the impedance of said line at carrier wave frequencies, a balanced transformer connecting said line and said means, a carrier wave transmitting channel and a 10 carrier Wave receiving channel conjugately connected to said transformer to prevent inipression of energy from the local transmitting channel upon the local receiving channel, and a current limiting device in said receiving channel to limit disturbing energy- 15 received thereby.

In witness whereof, I. hereunto subscribe my name this 5th day of August A. D., 1921.

HAROLD W, NICHOLS. 

